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Computational study of the working mechanism and rate acceleration of overcrowded alkene-based light-driven rotary molecular motors
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Computational Physics. Linköping University, The Institute of Technology.
2014 (English)In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 20, 10240-10251 p.Article in journal (Refereed) Published
Abstract [en]

In recent years, much progress has been made in the design, synthesis and operation of light-driven rotary molecular motors based on chiral overcrowded alkenes. Through consecutive cistrans photoisomerization and thermal helix inversion steps, where the latter dictate the overall rate of rotation, these motors achieve a full 360° unidirectional rotation around the carbon–carbon double bond connecting the two (rotator and stator) alkene halves. In this work, we report quantum chemical calculations indicating that a particularly fast-rotating overcrowded alkene-based motor capable of reaching the MHz regime, can be made to rotate even faster by the substitution of a rotator methyl group with a methoxy group. Specifically, using density functional theory methods that reproduce the rate-limiting 35 kJ mol−1 thermal free-energy barriers shown by the methyl-bearing motor with errors of 5 kJ mol−1 only, it is predicted that this substitution reduces these barriers by a significant 15–20 kJ mol−1. This prediction is preceded by a series of benchmark calculations for assessing how well density functional theory methods account for available experimental data (crystallographic, UV-vis absorption, thermodynamic) on the rotary cycles of overcrowded alkenes, and a detailed examination of the thermal and photochemical reaction mechanisms of the original motor of this type.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2014. Vol. 4, no 20, 10240-10251 p.
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-104688DOI: 10.1039/C3RA46880AISI: 000332061300048Scopus ID: 2-s2.0-84894247198OAI: oai:DiVA.org:liu-104688DiVA: diva2:698493
Available from: 2014-02-22 Created: 2014-02-22 Last updated: 2017-12-05Bibliographically approved
In thesis
1. Computational Design of Molecular Motors and Excited-State Studies of Organic Chromophores
Open this publication in new window or tab >>Computational Design of Molecular Motors and Excited-State Studies of Organic Chromophores
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents computational quantum chemical studies of molecular motors and excited electronic states of organic chromophores.

The first and major part of the thesis is concerned with the design of light-driven rotary molecular motors. These are molecules that absorb light energy and convert it into 360° unidirectional rotary motion around a double bond connecting two molecular halves. In order to facilitate potential applications of molecular motors in nanotechnology, such as in molecular transport or in development of materials with photo-controllable properties, it is critical to optimize the rates and efficiencies of the chemical reactions that produce the rotary motion. To this end, computational methods are in this thesis used to study two different classes of molecular motors.

The first class encompasses the sterically overcrowded alkenes developed by Ben Feringa, co-recipient of the 2016 Nobel Prize in Chemistry. The rotary cycles of these motors involve two photoisomerization and two thermal isomerization steps, where the latter are the ones that limit the attainable rotational frequencies. In the thesis, several new motors of this type are proposed by identifying steric, electronic and conformational approaches to accelerate the thermal isomerizations. The second class contains motors that incorporate a protonated Schiff base and are capable to achieve higher photoisomerization rates than overcrowded alkene-based motors. In the thesis, a new motor of this type is proposed that produces unidirectional rotary motion by means of two photochemical steps alone. Also, this motor lacks both a stereocenter and helical motifs, which are key features of almost all synthetic rotary motors developed to date.

The second part of the thesis focuses on the design and assessment of composite computational procedures for modeling excited electronic states of organic chromophores. In particular, emphasis is put on developing procedures that facilitate the calculations of accurate 0−0 excitation energies of such compounds in a cost-effective way by combining quantum chemical methods with different accuracies.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2016. 64 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1794
National Category
Theoretical Chemistry Organic Chemistry Chemical Sciences
Identifiers
urn:nbn:se:liu:diva-132611 (URN)10.3384/diss.diva-132611 (DOI)9789176856741 (ISBN)
Public defence
2016-12-15, Schrödinger (E324), Fysikhuset, Campus Valla, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2016-11-16 Created: 2016-11-16 Last updated: 2016-11-17Bibliographically approved

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Fang, ChangfengOruganti, BaswanthDurbeej, Bo

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